The present invention relates to valve bags that feature a self-closing valve which closes in response to pressure from the contents of the bag after filling. The contents are typically a powdered or granular medium. A valve bag is a container made with one or more tubular plies of material, the material usually being a rigid paper such as kraft paper. Typically, the valve bag ends are formed by cutting and folding the plies, thereby forming flaps on the long sides of the bag end. Flaps are also formed on the short sides of the bag end. The short flaps are folded inward and the long flaps are folded over each other on top of the short flaps, thus forming the end of the bag. These flaps may be glued or heat bonded together to seal the end of the bag. The bag is usually folded to form gussets extending from both short sides of the bag end resulting in a satchel-type rectangular configuration. These gussets may be folded inward or outward from the sides of the bag. When the bag is filled, these gussets unfold and cause the bag end, top or bottom, to take the rectangular shape. This type of bag is usually called a gussetted satchel bag.
A valve bag is most often a satchel bag which features a channel formed on one of the short sides of the filling end of the bag. This channel is typically a flattened tube which is inserted during bag manufacturing on one side of the bag end before the flaps are folded and sealed together. The channel may also be formed by leaving the two flaps on the long side of the bag end unsealed to the flap on the short side. The channel and the length of the flap on the short side form a passage, which allows access to the interior of the bag for filling it with contents. The folded short side flap may extend further into the bag than the channel, such as that disclosed in Kelley et al., U.S. Pat. No. 5,516,210, thus providing a closure or shutoff for the valve. The valve is closed by the contents of the bag pushing this flap against the sealed long side flaps of the bag end. When the prior art valves are closed, the contents of the bag are supposed to be prevented from sifting out of the channel. Thus, there is no need to immediately heat or sonically seal the bag after it is filled. This allows the bag to be sealed at another location on the production line in the filling process of the bag user.
The main goal of prior art sealable valve bags has been to prevent the sifting or leakage of the bag contents back through the channel of the valve after filling. This goal was addressed by the initial mechanical closing or sealing of the valve in order to prevent such sifting or leaking. Known sealable valve bags have utilized a valve formed from a flattened tube. This tube usually extends outward from the short side of the bag end in order to provide an adequate length of material for the sealing process. For the final sealing closure, the inner surface of the tube is typically coated with an adhesive or other sealing material, which may be activated by heat, pressure, or ultrasonic means. Other valve bag constructions rely on hot melt glue to provide a final seal to the valve. When the packer is ready, valve bags are filled by means of a filling nozzle which is inserted into the valve channel. When the bag is full, the nozzle is removed and the valve opening is then ready to be finally sealed.
While some of the sifting problems have been prevented by these previously used sealable valve bags, they still have limitations inherent in their structure. Sifting and spillage may yet occur when the filling nozzle is removed. This is partially due to the memory of the rigid valve material after removal of the nozzle. Prior art bags which were to be finally sealed at a remote location down the manufacturing line, distant from the filling point, spilled out product between these two stages of the process. Even valve bags which have had an extended short side flap in order to close off the valve channel, nonetheless have still allowed sifting around the sides of this flap, resulting in spillage through the valve opening during transport to the final sealing station. This spillage also affects the seal quality by contaminating any opposing sealing surfaces prior to the sealing process. Furthermore, since the prior art valve constructions have typically utilized only the plies of the bag to support the valve tube, they have been susceptible to tears or damage during the filling process.
It is therefore an object of the present invention to provide a sealable valve bag assembly, which upon filling, immediately creates a mechanical seal lock along the standard parallel fold lines of a satchel-type bag end at the bag-inward opening of the valve tube, thereby sealing both sides of the valve tube in the fold lines and eliminating any possible channeling of the bag contents through and alongside the valve tube prior to a final sealing step.
It is a further object of the present invention to provide a seal tab lock which extends beyond the innermost edge of the short side flap of the bag, thus creating a flap valve which purposely prevents filled product from escaping back out the valve tube before the valve is ultimately sealed by heat, sonic, pressure, adhesive means, or the like.
It is still another object of the present invention to provide a seal tab lock which is attached to the valve bag assembly, but not formed from the valve bag plies, thus adding strength and support to the valve side of the bag end in order to prevent tears or ruptures in the valve area during and after the filling operation.